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The rp2350 holds 4096 rows of 24 bit one-time-programmable memory, which the port did not expose at all. This adds a driver on the NuttX efuse interface, registered by the common board bringup as /dev/efuse. The driver uses the ECC interpretation of a row, in which 16 bits carry data and the remaining 8 carry a Hamming code, so the OTP appears as a flat space of 4096 * 16 bits for the efuse field descriptors to index: a descriptor at bit offset N refers to bit N % 16 of row N / 16. That matches the row numbers already listed in hardware/rp23xx_otp_data.h. Reads come from the chip's ECC-translated window and have no side effects. Rows are locked in pages of 64; a page locked against reads would raise a bus fault, so the lock is checked first and reported as an error instead. Programming needs the separate RP23XX_OTP_WRITE option, which defaults to off; without it a write returns EPERM and no programming code is built at all. When enabled, a row is programmed as a whole through the bootrom, since the ECC bits cover the whole row. For the same reason a row that already holds data cannot be modified, and such a write is rejected rather than left to corrupt the row's ECC. Assisted-by: Claude Opus 5 (1M context) <noreply@anthropic.com> Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com> |
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